Consumer appliances, such as refrigerators and stoves, have become a mainstay in nearly every American home. Continued advances in these appliances have resulted in the addition of many new features and functions. These new features and functions have increased both the efficiency and the reliability of the appliance, and have reduced the cost and time required to maintain and clean the appliance. One prime example of an appliance which has benefited from the continued advances in the consumer appliance industry is the stove. A modern stove now typically includes a warming feature, a broil feature, as well as a self-cleaning feature (a particularly time saving and desired feature). In addition to these new features, typical stoves still include a user selectable temperature setting which allows the baking of various dishes at various temperature settings. The continuously adjustable temperature setting allows the user to tailor the cook temperature to suit their desires and preferences, and the varying requirements of different recipes.
In the past, oven controls were primarily mechanical in nature. These early mechanical controls utilized a variable port gas valve which varied the amount of gaseous fuel delivered through the variable port to the oven burners in an attempt to regulate the temperature therein. Many advances have been made in the control of oven temperature and feature settings from these early mechanical control devices, including the utilization of electronic thermostatic control of the temperature within the oven compartment. Continued advances in the field of electronic controls have allowed further integration of control features, and have led to the single knob oven control. This single knob oven control, a front panel design of which is illustrated in FIG. 6 allows a user with a single rotary knob to select a particular cooking temperature by rotating the control knob until the indicator is pointing to the desired temperature as listed on the temperature scale 10 illustrated in FIG. 6. Additionally, this single rotary knob control allows the user to select the various functions, such as warm 12, clean 14, broil 16, or off 18 by simply rotating the control knob until the indicator points to the desired function. This single knob control has gained widespread acceptance, and is now quite popular.
These early electronic single knob controls typically utilized a potentiometer with internal switches such as is illustrated in FIG. 7. As this figure illustrates, the single knob oven control utilizes an integrated electrical circuit comprising a linear tapped potentiometer 20 and a series of internally positioned electrical contacts 22, 24, 26, and 28. Each of these electrical contacts form one side of a switch which, depending on the position of the rotary control knob (not shown), would establish connections between two of these electrical contacts (e.g., electrical contact 22 and electrical contact 24) to initiate a given feature of the oven (e.g., the broil feature).
While these single knob oven controls have gained widespread acceptance and consumer preference throughout the industry, the accuracy of operation of these early controls were somewhat limited. Specifically, and with continuing reference to FIG. 7, the nature of the slide type electrical contacts 22-28 require that a certain angular tolerance of between 18.degree.-20.degree. be provided to ensure that the proper feature was selected when the control knob was positioned to select that particular feature. Safety requirements dictated that the spacing between each of the feature selectable electrical contacts be in the range of 20.degree.-25.degree. to ensure "break-before-make" switching between features and to ensure that an improperly positioned control knob would not inadvertently or alternatively select multiple features. Unfortunately, these requirements for the electrical contacts 22-28 severely limited the angular range, and therefore the accuracy, of the temperature selecting portion of the potentiometer. Specifically, as illustrated in FIG. 7, the inclusion of three functions (broil, clean, and off) reduces the available angle for the potentiometer (used to select the cooking temperature) to a mere 235.degree. typically. The additional requirement of inter-functional spacing reduces the useful angular space of the potentiometer to only approximately 180.degree. from the warm temperature setting to the 500.degree. temperature setting.
This limitation on the useful resistance change versus the percentage travel around the knob is illustrated in FIG. 8. As may be seen from this figure, an ideal linearized potentiometer's resistance varies in accordance with line 30 from approximately 10.degree. (3.6% of travel) to approximately 245.degree. (68% of travel). However, as mentioned above, because of the inter-functional spacing requirements the actual useful variation of resistance is bound between the warm setting at line 32 and the 500.degree. temperature limit illustrated by line 34. As mentioned above, this limitation on the useful rotation of the single control knob reduces the accuracy of the actual temperature selection for baking conditions. In other words, because of the limited angular travel available to select the various cooking temperatures, a very small resistance change relates to a very large temperature change in the cooking compartment. As a result, normal mechanical tolerances on the mounting of the control knob could result in an unacceptably large deviation from the selected temperature to the actual oven compartment temperature during different bake cycles.
Recognizing this limitation as a problem and an area for customer dissatisfaction, the assignee of the instant invention developed a second generation single knob oven control which greatly improved the accuracy of the temperature selection portion of the single knob control by increasing both the physical angular area of the variable resistance potentiometer and the actual useable area as well. Such a second generation single knob oven control is described in U.S. Pat. No. 5,662,465 entitled "Controlling Flow of Fuel Gas to a Burner", issued Sep. 2, 1997, to Yoshio Kano and assigned to the assignee of the instant application, the disclosure and teachings of which are hereby incorporated by reference. This second generation single knob control, a typical embodiment of which is illustrated in FIG. 9, increases the potentiometer area to approximately 280.degree.. This second generation single knob oven control still utilizes the internal angularly positioned electrical contacts for selection of the various oven features. As discussed above, these angularly placed electrical contacts require a certain amount of angular tolerance to ensure proper initiation of each selected function, as well as a certain angular displacement between positions as described above. When these considerations are taken into account, the useable resistance variation for temperature control is reduced to approximately 265.degree.. While this second generation single knob oven control is a significant improvement over its predecessor, the inventors of the instant application have continued to seek out continued areas of improvement. However, further improvement in the useable angular area of the potentiometer is limited by the safety requirements and necessary mechanical tolerances on the feature select electrodes which are integral therewith.
One method of increasing the useable variable resistance of a potentiometer is to exclude the ability to select the various cooking features from the single knob oven control. However, as will be recognized by one skilled in the art, such a removal requires the inclusion of either a second rotary knob to perform the feature selection function, or the inclusion of separate push buttons to effectuate the same selection. While these alternate designs are being sold on ovens (for example the Hotpoint brand oven, model no. RB532GON4AD, includes a temperature selection knob and a oven feature control knob having the discreet positions of OFF, BAKE, BROIL, and CLEAN). However, as will be recognized by one skilled in the art, such an arrangement requires that the user access two separate controls to perform the simple baking function. If the user forgets to actuate both control knobs (first selecting the desired baking temperature followed by selection on a separate control knob of the bake function), the meal may well be delayed until the situation is realized. Likewise, if the user forgets to turn both knobs to OFF, the oven may remain heated until this situation is realized. Since most Americans are familiar with and expect single knob control of an oven, such a compromise is not desired. However, this compromise has been necessary in order to gain increased accuracy of the temperature selection and control of the oven. Until now.